Do you have any powerheads in your tank? I don't see any in the picture in your avatar. Powerheads have many functions, one of which is to move the water to oxygenate it. If you're finding you have swings in pH, it could be that you don't have enough flow in the tank.
It also looks like you have very little live rock. Most tanks have a pound or a pound and a half per gallon.
It seems like you've added a lot of fish very fast to the tank. I would suggest waiting at least a month to allow the tank to settle before thinking of adding any more.